I propose to characterize the basic visual abilities of children and adults with Williams Syndrome (WS), and of normally developing children. Williams Syndrome is a rare genetic disorder that has a distinct cognitive profile: a relative strength in language, but a profound weakness in visual-spatial cognition. This profile is of great interest because it suggests the possibility that genetic deficit might target specific cognitive systems, in this case, the system of spatial cognition. To date, most studies with WS have used complex visuo-motor tasks such as drawing or block construction to evaluate their visual-spatial abilities. Some have suggested that these deficits are not linked to "low-lever' visual functions such as stereopsis and acuity. However, very little is known about the abilities of WS in basic visual tasks. I plan to evaluate the possibility that the spatial cognitive deficits of WS are linked to important visual functions that allow integration of features over space. Using psychophysical tasks, I plan to look at how WS and normal controls detect a single object (e.g. detecting a grating at various spatial frequencies) as well as how they integrate multiple objects (e.g. detecting a contour made up of many gratings). These studies will give us a better understanding of how simple visual functions may contribute to complex spatial cognition deficits in WS, and perhaps provide insight into possible therapies that could ameliorate WS deficits. Furthermore, they will uncover the developmental trajectory of feature detection and feature integration in normal children.